perf: 优化任务执行速度 (40-70s → ~15s)

问题：容错机制引入了大量叠加的等待时间

优化内容：
- playwright_automation.py:
  - 登录超时 30s → 10s
  - 导航等待 2s → 0.5s
  - navigate_only 等待 1s → 0.3s
  - 首页轮询 8次×3s → networkidle + 2次×0.5s
- services/tasks.py:
  - 删除截图前固定 sleep(2)
- services/screenshots.py:
  - networkidle 超时 30s → 10s
  - selector 超时 20s → 5s

预计性能提升：从 40-70 秒降至约 15 秒

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/tasks.py

@@ -857,7 +857,6 @@ def run_task(user_id, account_id, browse_type, enable_screenshot=True, source="m
                             },
                         },
                     )
-                    time.sleep(2)
                     browse_result_dict = {"total_items": result.total_items, "total_attachments": result.total_attachments}
                     screenshot_submitted = True
                     threading.Thread(